Terrestrial communication system using satellite transmission techniques

ABSTRACT

A terrestrial communication system, facilitating audio, video, data, and any other type of communication within a local geographical area, and with an extremely large number of communication channels being made available simultaneously at a very low cost. It comprises at least two local terrestrial satellite (LTS), preferably located in a mast or any other supporting structure, each LTS having high frequency communication equipment substantially corresponding to a conventional geostationary satellite for digital transmission of video, audio, or data, arranged to transmit in the L Band (1-2 GHz), the S Band (2-4 GHz), or a high frequency band with a relatively low power output and having a preferably omnidirectional antenna installation for transmission in a substantially horizontal plane. The signals can be digitalized according to MPEG-2 or according to any known signal algorithm.

TECHNICAL FIELD

The present invention relates to a terrestrial communication system,facilitating audio, video, data, and any other type of communicationwithin a local geographical area, and with an extremely large number ofcommunication channels being made available simultaneously at a very lowcost.

BACKGROUND ART

Audio, video, and data communication are rapidly increasing sectors ofinterest, and existing terrestrial communication circuits, radiocommunication channels and satellite communication systems are usedextensively. Dedicated cable systems are also being used to cover localgeographical areas with a large number of TV-channels, and these cablesystems may also be used for data transmission purposes.

Digital transmission techniques have been developed, and as a result,digital consumer TV transmissions are now available from satellitetransponders, and due to the digital techniques utilized, the number ofprograms transmitted by each transponder is no longer one program only,since several programs can be transmitted simultaneously by eachtransponder.

However, with regard to terrestrial transmissions techniques, a suitablesystem has not yet been developed, but it is hoped that such a dedicatedsystem will be made available within the next few years. This willrequire development of suitable encoders and decoders, specificallydeveloped for terrestrial digital transmission techniques and frequencybands today used for terrestrial TV transmission purposes. Considerableefforts and large sums of money have been invested in the development ofsuitable techniques, but so far, these efforts have not been successful.

DISCLOSURE OF THE INVENTION

The present invention is based on the discovery that present satellitetransmission techniques also can be used for terrestrial transmission.

As a result, a user having equipment intended for reception of digitalsatellite signals can also use the very same equipment for reception ofterrestrial transmissions. This is achieved by arranging communicationequipment of the type used in satellites as Local Terrestrial Satellites(LTS) in a mast or other suitable foundation. Transmission from a LTS isbased on one of the conventional standards for digital transmission astoday used by conventional orbiting geostationary satellites, e.g.,MPEG-2 or MPEG-1 or any other standard suitable for audio, video or datatransmission purposes. A preferred standard today is frequency modulatedMPEG-2 (also compatible with MPEG-1), but other known or futurestandards may also be used, and amplitude modulated (AM) transmissiontechniques can also be used as an alternative to frequency modulated(FM) transmission techniques. Each LTS is transmitting using relativelylow output power and with an antenna arrangement preferably having noneor little directional effect. As a result, a suitable number of LTS canbe arranged to cover a local geographical area, giving the inhabitantsaccess to individual communication channels for data, video (TV), andaudio communication. The advantages of such a system will be more fullydiscussed later.

The terrestrial communication system according to the present inventioncomprises at least one local terrestrial satellite (LTS), preferablylocated in a mast or any other supporting structure, each LTS havinghigh frequency communication equipment substantially corresponding to aconventional geostationary satellite for digital transmission of video,audio or data, arranged to transmit in the L Band (1-2 GHz), the S Band(2-4 GHz) or a higher frequency band with a relatively low power outputand having a preferably omnidirectional antenna installation fortransmission in a substantially horizontal plane.

BRIEF DESCRIPTION OF DRAWINGS

A number of non-restricting examples of embodiments according to thepresent invention will be more fully described with reference to theaccompanying drawings, in which:

FIG. 1 is a view from above diagrammatically showing a basic systemaccording to the invention, including only one local terrestrialsatellite (LTS) and two users of the system;

FIG. 2 is a diagrammatically shown side view of a mast arranged tosupport two LTS at different heights;

FIG. 3 is a side view diagrammatically showing a system according to thepresent invention, which theoretically illustrates how a large number ofLTS can be disposed in a circular arrangement;

FIG. 4 is a view from above of four LTS in a square arrangement,indicating the zone where users may communicate with any one of thesefour LTS;

FIG. 5 is a side view of a number of masts, each one supporting a LTS,intended to illustrate how the masts or any other supporting structurecan be more closely located to each other; and

FIG. 6 is a diagrammatically view from above, disclosing how a number ofLTS may be linked together for internal communication.

MODES FOR CARRYING OUT THE INVENTION

As previously mentioned, the present invention is based on the discoverythat present communication techniques used for digital satellitecommunication purposes also may be used for terrestrial communicationpurposes. This fact has not been realized previously, and consequently,all research efforts have been directed to the development ofalternative techniques, facilitating digital transmission within theconventional TV-channel system.

According to the present invention, communication equipment of the typepresently used in modern earth orbiting communication satellites isarranged in a mast or any other suitable structure, thereby forming alocal terrestrial satellite (LTS). The transponders are connected to anomnidirectional antenna system, and the parties using the systempreferably utilize parabolic antennas which can be directed towards saidomnidirectional antenna system.

A simple system of the above type is diagrammatically shown from abovein FIG. 1, showing a LTS with a substantially circular andgeographically restricted coverage, the border of which is denominatedas 1, and a number of parabolic antennas 2, 2′, each being connected toequipment 3, 3′ of the type used for receiving and decoding digitalsignals of the same type as transmitted from conventional satellites.The output from this type of equipment 3, 3′ is advantageously fed to acomputer and a video signal may be viewed on a monitor, TV-screen or anyother means, with the audio signal converted into audio from aloudspeaker system. With regard to data communication, same may bemulti-directional, i.e., a computer with relevant equipment forreception/transmission of signals may receive and transmit signals froma computer to the LTS, and thus communicate either with other computersconnected to the LTS or with other communication systems communicatingwith the LTS.

The above discussed system is a basic system, i.e., only one LTS isdisclosed. However, the number of LTS within a local geographical areamay be increased as desired, thereby increasing the number ofcommunication channels substantially indefinitely.

This can be accomplished by arranging more than one LTS in a mast orother supporting structure, separated by a suitable vertical distance.This is shown diagrammatically in FIG. 2. Furthermore, such masts orsupporting structures may also be arranged horizontally spaced from eachother (as diagrammatically illustrated in FIG. 3), and provided that auser has a suitable directional antenna installation, e.g., a parabolicantenna or a multi-beam directional antenna, the antennas connected tothe transponders of utilized LTS only require to be spaced apart a fewdegrees in relation to the location of a user to reduce interferencefrom adjacently located LTS to an acceptable level (with interferencefrom an adjacent non-selected LTS substantially reduced to nil).

Communication between transponders of utilized LTS and the usersinvolves low output power transmission, typically an output power of 2-5Watt is sufficient, even though increased output power also can be used.High frequency band transmission is also used, preferably starting atthe S Band range 2-4 GHz but ranging up to 400 GHz. However,transmission can also take place outside these limits, e.g., within theL Band (1-2 GHz).

Low output power in combination with high frequency transmission makesit possible to restrict transmission to a predetermined restricted localgeographical area. By increasing/reducing transmitted output power, thearea covered by a LTS can be modified as desired. Modifications to theantenna system can also be used, in particular if interference shouldoccur between two or more LTS having different locations, whereby outputin non-desired direction(s) can be reduced as an alternative toreduction in output power.

Problems with interference between geostationary earth orbitingsatellites and a LTS in the system according to the invention do notoccur, since the LTS are located below the arc at the horizon defined bythese satellites. Accordingly, transmitted signals from thesegeostationary satellites can be received without interference fromLTS-transmitted signals on the very same frequency, since the receivingparabolic antenna has an increased angle to the horizontal plane whenarranged to receive signal from an earth orbiting satellite as comparedto an antenna intended for reception of signals from a LTS.

The system according to the present invention makes it possible within alocal geographical area to obtain a considerable number of communicationchannels. It is known that the difference in the location ofgeostationary satellites only need to be in the region of 2°-3° in orderto avoid interference between channels transmitted with the samefrequency. Even if this angular difference is increased to 6° for asystem according to the present invention, this would result in 60(360°/6) LTS-locations when arranged located circular as shown in FIG.3. Should each mast or any other structure supporting the localterrestrial satellites be arranged to support three individual LTS(located high, very high, and extremely high), the number of LTScovering a predetermined restricted geographical area would be increasedto 180 (3×60), whereas an arrangement with two LTS increases the numberto 120 (FIG. 2). Each single LTS can transmit approximately 5,000TV-programs of acceptable quality, and as a result, the system accordingto the present invention may simultaneously transmit 900,000 (180×5,000)different TV-programs within a local district, without interferenceproblems. This number may actually be further increased, since the LTSmay also be arranged alternating high-low in relation to the groundplane (as disclosed in FIG. 5), whereby each point of location may beeven closer than the one shown in FIG. 3. The circular configuration ofFIG. 3 can be replaced by any other configuration, and a further exampleis shown in FIG. 4.

With regard to equipment for reception of signals from a LTS, presentlyused parabolic dishes and satellite receivers with digital decoders canbe used, provided that the frequencies of channels transmitted from theLTS fall within the same frequency range as used by presentgeostationary satellites. Accordingly, no additional expensive equipmentwill be required by the users for reception of TV or text TV, the onlymodification required would be to direct the parabolic dish antennatowards the LTS.

With regard to TV programs transmitted via the system according to thepresent invention, it is obviously possible to arrange a LTS used for TVtransmission purposes connected to parabolic dishes and receivingequipment for programs transmitted from orbiting geostationarysatellites, and retransmit these programs via the LTS. As a result, auser would gain access to all these channels without the normallyrequired large diameter dish antenna and the control system facilitatingrotation of the in order to locate and receive signals from variousgeostationary satellites having in relation to each other differentpositions. Pay channel programs can be requested by users of the system,and charged for the time viewed.

Another interesting feature with the system according to the presentinvention is the possibility of real “video on demand”. The use ofdigital transmission techniques and “smart cards” has today made itpossible to offer users of existing geostationary satellite systems thepossibility to view certain programs on demand, e.g., movie films.However, the present systems involve transmission of films at certainpredetermined hours, and a user can call the operator by telephone,requesting one of the films running at such a starting time. A specificsignal is sent to the user, whereby the decoder (or a smart card) isactivated to decode the requested film as from the starting time untilthe end of same. The cost for viewing this particular film is billed tothe user. However, this can not be regarded as real video on demand,since the user is restricted to make a choice between a restrictednumber of films and the user must also accept predetermined startinghours.

Due to the large number of channels available in a system according tothe present invention, video on demand can be offered which really meetsany requirement by a user. Any desired film can be ordered, e.g., bytelephone, as well as any starting time. When ordering, the userreceives information of the channel number to be used, e.g., 28F. Theoperator has access to a video film library, e.g., by satellitecommunication, and may from any other part of the world obtain thedesired film, transferred in digitalized form at a high speed and storedby the operator on a suitable storage medium, e.g., a hard disc storagedevice. This means that any film available in the world can be viewed atany desired time by an individual user, and the costs involves can berealized to a specific user.

As previously mentioned, the system according to the present inventioncan also be used for data communication purposes. A computer can thus,suitably equipped with transmitting and/or receiving equipment connectedto an antenna system be arranged to communicate with a LTS. For example,communication via Internet can be established facilitating high speedcommunication, and with speeds unavailable via telephone circuits. Thelink from the LTS can be obtained via an earth orbiting geostationarysatellite, cable, a LTS link system (to be discussed later), or anyother suitable method. Such a computer may also be used as a TVreceiver, or be linked to a separate monitor used as a TV screen.

As mentioned above, the system according to the present invention mayalso be used with one or more of included LTS being part of aterrestrial link system. By including a preferably directional type ofantenna in the antenna system, directed towards a second LTS, preferablyalso having a similar type of antenna directed towards the first LTS, alink can be established between the same. Said second LTS may bearranged in a manner similar to the first LTS in order to communicatewith a third LTS, which in turn is equipped to communicate with a fourthLTS, and so on (FIG. 6). Local districts may thus be interconnected toeach other and/or links can be established for long distance data, videoor audio communication and/or communication with suitable centres givingaccess to communication cable networks or satellite communication or anyother desired function.

It is also within the scope of the present invention to use the LTS forpure audio communication, i.e., a user may contact a LTS by means of asmall transceiver in order to establish verbal contact with another userhaving similar communication equipment. Furthermore, the LTS can also beconnected to a public telephone network, whereby a user with equipmentsubstantially similar to a cellular telephone can initiate or receivetelephone calls.

The type of LTS used in the system for terrestrial communicationaccording to the present invention has not been described in detail, butcomprises of the communication equipment as known to a person skilled inthe art as suitable for a communication satellite in earth orbit,normally referred to as a geostationary satellite. The antenna system isnormally of omnidirectional type, but may, as mentioned earlier, alsoinclude antennas for certain purposes having a more or less directedlobe. The equipment for reception of signals from a LTS includespreferably equipment similar to what is used for reception of signalsfrom geostationary satellites using digital transmission techniques. Anadvantage of the present system is that the directional dish antennarequired can be made very small as compared to dishes used for receptionof signals from geostationary satellites. A preferred signallingtechnique is MPEG-2, but as stated earlier, any other known or futuredigital transmission technique can be used, including the earlierversion of MPEG (MPEG-1). Frequency modulation (FM) is a preferredmodulation technique, but amplitude modulation (AM) can also be used.

The above given examples of use for the system according to the presentinvention are only intended to disclose some of the applicationspossible with the system according to the present invention. However,fields of use are in no way restricted to these examples, since thepresent invention opens up new and previously unknown possibilities dueto the extremely large number of communication channels made availablein any certain area and without problems with interference from otherchannels or transmitters (due to the short range of the signals and thedirectivity of the antennas used for reception purposes). The LTSincluded in the system can advantageously make use of existing masts andother high structures, and the low cost of an LTS makes it possible toimplement the system according to the present invention at very lowcosts. Reception of TV programs only requires today existing and widelyavailable equipment as used for reception of signals from geostationarysatellites.

The possibility of two-way communication from a computer to a LTS opensup the field of communication for companies, local authorities and otherparties, and an individual may communicate with local shops and otherlocal businesses, i.e., to place orders and make purchases.

All this is accomplished using low cost equipment and well testedtechniques, resulting in an enormous availability of communicationchannels/frequencies within a restricted and local geographical area.

INDUSTRIAL APPLICABILITY

The system according to the present invention solves the problem ofterrestrial transmission of digital video, audio, and data signals.Existing satellite receiving TV-sets may without additional equipment ormodifications receive signal thousands of TV-channels from one of theLTS included in the system. Cable TV systems thus become obsolete, dueto the low number of programs which can be transferred via cable, andalso due to the initial costs for establishing a cable network. Allproblems with “shadows” (echoes) existing in conventional terrestrial TVsystems are also avoided.

Furthermore, the system may be used for data communication purposes,whereby the communication speed is increased to speeds equivalent of alocal area network (LAN). For example, in a municipality, the datasystem of the local administration can be accessed from schools, rescueservice, and other local services without the need for a local highspeed cable system. Local TV can be made available for all inhabitantsat an extremely low cost.

Local systems according to the present invention may also serve asrepeaters for TV programs transmitted from geostationary satellites orterrestrially transmitted TV programs, and local systems may also belinked together in a network.

The availability of such a large number of channels/frequencies at sucha low cost opens up previously unknown possibilities to use informationtechnology (IT) for novel and valuable purposes, e.g., education, localshopping, video on demand, working (distance working from home), highspeed Internet communication, and may other fields of use.

What is claimed is:
 1. A terrestrial communication system facilitatingone way and/or two-way audio, video or data communication for userswithin a restricted geographical area with use of frequencies within themicrowave range and a relatively low power output, characterized in,that the system comprises at least two local terrestrial satellites(LTS) having high frequency communication equipment substantiallycorresponding to a conventional geostationary satellite utilized digitaltransmission techniques, the antenna system of each LTS being locatedspaced from remaining LTS serving the geographical area to be covered,said antenna system being preferably omnidirectional and arranged fortransmission in a substantially horizontal plane, users of the systemhaving directional antenna installation being able to select desired LTSby a change of the directional antenna in an horizontal, rotary plane orvertical plane of inclination thus facilitating that frequencies used byone LTS of the system also are being used by any other LTS included inthe system for similar or different communication purposes, therebyincreasing the number of communication channels available within a givenfrequency segment to a substantially unlimited number of channels byinclusion of further LTS covering an intended geographical area.
 2. Aterrestrial communication system according to claim 1, characterized in,that the antenna system of at least two adjacently located localterrestrial satellites (LTS) are supported spaced from each other atdifferent heights in a mast or any other structure supporting the same,sufficiently spaced from each other to facilitate transmission and/orreception of signals at any channel frequency with regard to usershaving directional antenna systems with a certain degree of inclination,without undue interference from other signals transmitted and/orreceived at the same frequency from antenna systems located at differentheight, thus facilitating simultaneous multiple use of any one frequencyutilized by the system.
 3. A terrestrial communication system accordingto claim 1, characterized in, that the geographical location inhorizontal plane of adjacently located local terrestrial satellites(LTS) covering substantially or partly the same geographical area arelocated spaced from each other sufficiently to facilitate transmissionand/or reception of signals at any given frequency with regard to usershaving directional antenna systems without undue interference fromsignals transmitted and/or received at the same frequency from localterrestrial satellites (LTS) having a different geographical location,thus facilitating simultaneous multiple use of any one frequencyutilized by the system.
 4. A terrestrial communication system accordingto claim 1, characterized in, that the number of communication channelswithin a specific geographical area and with a given number ofcommunication frequencies is increased by an increased of the number oflocal terrestrial satellites (LTS) covering said specific geographicalarea each local terrestrial satellite (LTS) reusing said given number ofcommunication frequencies which is the number of available communicationchannels equalling the given number of frequencies multiplied by thenumber of local terrestrial satellites (LTS).
 5. A terrestrialcommunication system according to claim 1, characterized in, that thelocal terrestrial satellites (LTS) are arranged to be connected to asystem for video film distribution, and that any video film availablewithin such a system can be requested for individual viewing at anydesired time by a user of the system.
 6. A terrestrial communicationsystem according to claim 1, characterized in, that the localterrestrial satellites (LTS) are arranged to be connected to a systemfor communication with geostationary satellites, and arranged to serveas repeaters for signals received from or transmitted to saidgeostationary satellites.
 7. A terrestrial communication systemaccording to claim 1, characterized in, that at least one localterrestrial satellite (LTS) is arranged having cable connection to adata communication network, a public or private telephone network orcable network.
 8. A terrestrial communication system according to claim1, characterized in, that signals transmitted from and/or received bythe local terrestrial satellites (LTS) are digitalized according toMPEG-2, or according to a signal algorithm.
 9. A terrestrialcommunication system according to claim 7, characterized in, that thegeographical area covered by each local terrestrial satellite (LTS) isincreased or reduced as required by adjustment of the output power. 10.A terrestrial communication system according to claim 1 characterizedin, that at least two local terrestrial satellites (LTS) are arranged tobe communicating with each other, preferably having directional antennasystems for this purpose.
 11. A terrestrial communication systemaccording to claim 1, characterized in, that the system is preferablyarranged to operate within the L band or the S band, or at frequenciesbelow 25 GHz.